Detoxification studies using noxious lipophilic foreign and endogenous compounds, sometimes following metabolism by monooxygenase activity, have continued with conjugation reactions by genetically regulated (at the Ah locus) and phenobarbital inducible UDP glucuronosyltransferase activities. Substrates used for the transferases included 3 endogenous and 6 exogenous substrates. In attempts to distinguish the number of different transferases involved, UDP glucuronosyltransferase has been purified from phenobarbital-treated C57BL/6N mice by hydrophobic, anion exchange and affinity chromatography to homogeneity as defined by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). The purified protein conjugates at least 6 substrates and has a subunit molecular weight of about 51,000 daltons. In addition transferase studies have continued with established cell lines. Aryl hydrocarbon hydroxylase and 3-hydroxybenzo(a)pyrene transferase are induced or are not induced in parallel in the hepa-1 established cell line and 4 of its mutants by polycyclic aromatic compounds or phenobarbital.